1. Field of the Invention
The present invention relates generally to an optical position sensor for detecting a position of a moving object. More specifically, the invention relates to an optical position sensor which can avoid influence of variation of luminance level of a light beam. Further particularly, the invention relates to an optical position sensor which is suitable to use for monitoring angular position of an automotive steering, a crankshaft and so forth.
2. Description of the Background Art
Conventionally, optical position sensors have been used in various fields. Typically, the optical position sensor comprises a light emitting element such as LED and a photo sensing element, such as a phototransistor. The light emitting element and the photo sensing elements are coupled to form a photo-interrupter with a gap defined therebetween, through which a moving object moves. In the automotive technologies, such optical position sensors have been employed as a crank angle sensor, a steering angle sensor, a wheel speed sensor and so forth. However, such conventional optical position sensor is not satisfactorily precise in detecting the moving object. Namely, accuracy of detection of the position of the moving object is affected by fluctuation of luminance level of the light emitting element, offset of the trace of the moving object relative to the sensor and other various factors. Such noise factors tends to cause variation of luminance level distribution to cause shifting of transition point between HIGH level and LOW level of the sensor output.
In case of the optical position sensor employed in the automotive vehicle for monitoring the steering angle sensor, crank angle sensor or wheel speed sensor, it is essential to detect a light interruptor formed on a rotary body for accurately measuring steering angular displacement from a neutral position, crankshaft rotation speed or a road wheel rotation speed. Particularly, in order to facilitate precise control for the vehicular component, such as engine, brake system, suspension system and so forth, high precision level in monitoring the steering angular position, crankshaft angular position and rotation speed of road wheel becomes essential.